As the development of nanoscale mechanical, electrical, chemical and biological devices and systems increases, new processes and materials are needed to fabricate nanoscale devices and components. Optical lithographic processing methods are not able to accommodate fabrication of structures and features at the nanometer level. The use of self assembling diblock copolymers presents another route to patterning at nanometer dimensions. Diblock copolymer films spontaneously assembly into periodic structures by microphase separation of the constituent polymer blocks after annealing, for example by thermal annealing above the glass transition temperature of the polymer or by solvent annealing, forming ordered domains at nanometer-scale dimensions. Following self assembly, one block of the copolymer can be selectively removed and the remaining patterned film used, for example, as an etch mask for patterning nanosized features into the underlying substrate. Since the domain sizes and periods (Lo) involved in this method are determined by the chain length of a block copolymer (MW), resolution can exceed other techniques such as conventional photolithography, while the cost of the technique is far less than electron beam (E-beam) lithography or EUV photolithography, which have comparable resolution.
The film morphology, including the size and shape of the microphase-separated domains, can be controlled by the molecular weight and volume fraction of the AB blocks of a diblock copolymer to produce lamellar, cylindrical, or spherical morphologies, among others. For example, for volume fractions at ratios greater than about 80:20 of the two blocks (AB) of a diblock polymer, a block copolymer film will microphase separate and self-assemble into a periodic spherical domains with spheres of polymer B surrounded by a matrix of polymer A. For ratios of the two blocks between about 60:40 and 80:20, the diblock copolymer assembles into periodic cylindrical domains of polymer B within a matrix of polymer A. For ratios between about 50:50 and 60:40, lamellar domains or alternating stripes of the blocks are formed. Domain size typically ranges from 5-50 nm.
Researchers have demonstrated the ability to chemically differentiate a surface such that some areas are preferentially wetting to one domain of a block copolymer and other areas are neutral wetting to both blocks. Periodic cylindrical structures have been grown in parallel and perpendicular orientations to substrates within trenches by thermal annealing cylindrical-phase block copolymers. A primary requirement for producing perpendicular cylinders is that the trench floor must be non-preferential or neutral wetting to both blocks of the copolymer. For producing parallel-oriented half-cylinders, the trench floor must by preferentially wetting by the minor copolymer block.
A film composed of periodic hexagonal close-packed cylinders, for example, can be useful in forming an etch mask to make structures in an underlying substrate for specific applications such as magnetic storage devices. However, many applications require a more complex layout of elements for forming contacts, conductive lines and/or other elements such as DRAM capacitors.